Clean up sparse warnings

Mostly by adding static and removing excess extern qualifiers.  Also
convert a few remaining non-ANSI function declarations to ANSI.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/debugfs/util.c b/debugfs/util.c
index 09088e0..aafbc56 100644
--- a/debugfs/util.c
+++ b/debugfs/util.c
@@ -211,7 +211,7 @@
  * Parse a string as a time.  Return ((time_t)-1) if the string
  * doesn't appear to be a sane time.
  */
-extern time_t string_to_time(const char *arg)
+time_t string_to_time(const char *arg)
 {
 	struct	tm	ts;
 	time_t		ret;